High-power harvesting of mechanical energy from human locomotion is a well known concept which has not been commercialized in the past due to the lack of a viable energy harvesting technology. Classical methods of mechanical-to-electrical energy conversion (such as electromagnetic, piezoelectric, and/or electrostatic) are not well suited for direct coupling with the forces and displacements typical in human locomotion. For example, the highly restricted size and form-factor of a footwear-embedded device prevents the use of traditional, mechanical transducers that are necessary to convert a broad range of aperiodic forces and displacements (typically encountered in locomotion) into a readily accessible form.
Recently, a new approach to energy harvesting using microfluidic devices that substantially alleviates the above-mentioned problems has been demonstrated. In particular, a high-power microfluidics-based energy harvester is disclosed in U.S. Pat. No. 7,898,096, entitled METHOD AND APPARATUS FOR ENERGY HARVESTING USING MICROFLUIDICS, inventor: Thomas Nikita Krupenkin, granted Mar. 1, 2011, and in U.S. Pat. No. 8,053,914, entitled METHOD AND APPARATUS FOR ENERGY HARVESTING USING MICROFLUIDICS, inventor: Thomas Nikita Krupenkin, granted Nov. 8, 2011, both of which are incorporated by reference herein in their entirety. The energy harvester as disclosed in these references generates electrical energy through the interaction of thousands of microscopic liquid droplets with a network of thin-film electrodes and is capable of providing several watts of power. In one preferred embodiment of described in U.S. Pat. Nos. 7,898,096 and 8,053,914, a train of the energy-producing droplets is disposed within a thin channel (creating what will be referred to as an “energy-producing channel”) and is hydraulically actuated by a pressure differential (such as, for example, the movement of a foot) applied between the channel ends. Such an energy generation method provides an important advantage as it allows for efficient, direct coupling with a wide range of high-power environmental mechanical energy sources (including human locomotion).
A new method for energy harvesting using microfluidic devices that improves on the teaching of U.S. Pat. Nos. 7,898,096 and 8,053,914 has also been under development by the inventors and provides a new energy generation method and an apparatus that combine in a synergetic way the microfluidic-based electrical energy generation method based on the energy-producing channel concept and described in U.S. Pat. Nos. 7,898,096 and 8,053,914 with the classical magnetic method of electrical power generation based on Faraday's law of electromagnetic induction. One preferred embodiment of this method, as described in U.S. patent application Ser. No. 13/692,062, filed Dec. 3, 2012 and herein incorporated by reference, comprises a chain of special energy-producing elements (these elements being a set of magnets interleaved with a set of microfluidic droplets) which is adapted to freely slide along the energy-producing channel under the influence of a pressure differential applied between the channel ends as the result of hydraulic actuation. The energy-producing channel is formed to include alternating sets of dielectric members (which create energy when aligned with the microfluidic droplets) and electrical conductors (which create energy when aligned with the magnets). Energy generation is achieved by reciprocating motion of the chain within the energy-producing channel. Other preferred embodiments also utilize hydraulic actuation and includes the use of specialized expandable chain elements that allow for continuous revolving motion of the chain of energy-producing elements within the energy-producing channel. The resulting approach has a number of substantial advantages over the teaching of U.S. Pat. Nos. 7,898,096 and 8,053,914. In particular, it provides greatly increased power output and allows effective energy generation without the need for the external bias voltage source. This improves the harvester performance characteristics, enhances its reliability and simplifies the harvester design in comparison with the teaching of U.S. Pat. Nos. 7,898,096 and 8,053,914.
However, these methods of energy generation are not free from some shortcomings. In particular, in order to be compatible with conventional footwear, the energy-producing channel in these arrangements has to be flexible. This requirement, however, imposes severe restrictions on the dimensional stability of the energy-producing channel, as well as the chain of energy-producing elements. In particular, as the channel flexes (such as under the force of human locomotion), the channel walls alternately stretch and compress. This means that the relative position and spacing of the electrodes and coils embedded in the channel walls is dynamically changing, potentially creating misalignment between the energy-producing channel elements (electrodes and coils) on one side, and the chain of the energy-producing elements (magnets and microfluidic droplets) on the other side. This misalignment adversely affects power generation and thus leads to a lower energy harvesting efficiency. The problem equally affects both the reciprocating motion embodiments and the revolving motion harvester embodiments of the above-referenced arrangement.
Thus, need remains for a method and an apparatus that can preserve accurate alignment between the energy-producing chain and the coils/electrodes embedded in the channel walls (i.e., the “energy-producing channel”), without compromising the flexibility of channel itself, thereby improving the energy harvester device power output and increasing its efficiency.